A wireless terminal communicates to another party through a wireless communications system ("WCS"), which generally consists of a switch, and one or more base stations. The switch provides switching services for both wired as well as wireless users, and can be a Private Branch Exchange ("PBX"), Local Exchange Carrier ("LEC") or an Interexchange Carrier ("IXC") or any combination thereof. The base station is a wireless base controller, which has wired connection to the switch, and has one or more antenna to provide wireless connectivity to wireless terminals. A cell represents the coverage area provided by the antenna. The wireless terminal can be a single line or multi-line portable wireless telecommunications equipment that is connected to the WCS. A typical WCS consists of several cells that are adjacent, and are to a certain extent overlapping. A wireless terminal is associated with (or location registered to) the WCS through a particular cell in the WCS at any given time, where location registration is the procedure by which the wireless terminal informs the fixed part of the WCS its location within the system.
Mobility to a wireless terminal user is provided by linking the wireless terminal to the new adjacent cell, and handing off the call from the previous cell to the new one, thus providing call continuity. However as detailed below, maintaining call continuity is a difficult process. In a wireless environment it is difficult to define the boundaries of a cell and the associated coverage area. As a result, wireless installations can not provide total and perfect coverage. Gaps or holes in any system's wireless coverage is a very common phenomenon. In addition, a variety of interferences (both temporary and permanent) can arise which will affect wireless connectivity, including metal barriers or obstructions to wireless transmissions, interference by other wireless systems in the same coverage area, etc. Interferences caused by temporary obstructions are quite unpredictable. As such, existing handover mechanisms are not capable of providing call continuity in all of these circumstances.
The following are examples of scenarios in a wireless telecommunications environment where call continuity can not be provided by present handover mechanisms: 1) when the wireless terminal user temporarily moves out of the system's coverage area and then moves back in; 2) when the wireless terminal user moves between unsynchronized cell clusters within the system (as is common in a campus-like environment, where there are several geographically scattered buildings and it is expensive as well as difficult to provide contiguous or uninterrupted and synchronous coverage); and 3) when the wireless terminal user who is on a call experiences low battery power, and would like to replace it without having to disconnect the call.
In the scenarios described above or any other similar problem scenarios, handover of wireless calls will not happen since such a handover requires synchronized cells that provide total coverage throughout the system, without any interferences or gaps in the coverage and continuous/uninterrupted association of the wireless terminal with the WCS for the whole duration of a call. The wireless terminal user active on a call will experience some noises, pops and clicks, etc. due to a weak wireless connection, and eventually will lose link with the WCS. The WCS will get a message or an indication that it has lost the link with the wireless terminal. Since calls can not be recovered through handover, the WCS will drop the calls. As such, the wireless terminal user will have to manually re-establish a new call.
An existing procedure for re-establishing calls to wireless terminal users where handovers can not happen is termed automatic call back ("ACB"). In accordance with this procedure, when a wireless terminal, which has established a communication path with another party loses sync with the system, the call gets dropped at both parties on the call, but the call-related information is preserved by the system. When the wireless terminal user re-links with the system, the WCS places a new call to the wireless terminal first. When the wireless terminal user answers the call, the other party is alerted for the call. However, in this procedure both parties have to take some action to answer the call in order to re-establish the connection.
There are several major additional drawbacks with this approach. First, user action is involved at both ends of the call. That is, the procedure is not fully automated. The ACB procedure works only in a 2-party call scenario, and not in multi-party conference call scenarios. Furthermore, ACB requires that the wireless terminal be currently active on a call, to be reconnected (i.e., it does not reconnect a wireless terminal which has calls that are held, ringing, etc.). The ACB solution is limited to only one call at time, since it is a call-based reconnection and not a user-based reconnection where all calls at the wireless terminal are reconnected. Thus if there are multiple calls at a wireless terminal user, only the currently active call is restored, and all the other calls are dropped. Also, if two wireless terminals are connected to each other, both experience interference and both lose connection with the WCS, ACB will not be able to restore the call, since user action is required by both parties.
Accordingly, there is a need to provide a system, apparatus and method of automatically reconnecting all calls to a wireless terminal when a communications link carrying the call(s) is disconnected, without the limitations associated with the prior art.